1. Field of the Invention
This invention relates to an industrial robot system in which a robot deals with workpieces at a plurality of work stations in a predetermined order, and more particularly to an industrial robot system in which a robot which moves on rails can be accurately positioned at selected work station.
2. Prior Art
In a conventional industrial robot system of this type, a robot is moved on rails installed on a drive path which is formed on a concrete floor, and a rack secured to the drive path is engaged with a pinion of the robot. In the system, this robot is controlled according to the number of revolutions of the pinion which is turned as the robot travels, so that the robot is positioned in place at the work stations installed on the concrete floor, to handle workpieces at the work stations, e.g., to machine or assemble them.
In the conventional industrial robot system, the number of revolutions of the pinion of the robot, corresponding to the distances between a reference point on the traveling stand and a predetermined point at each of the work stations have been stored in a control unit in advance, so that the robot is moved, under control, to positions at the work stations in a predetermined order. However, the conventional industrial robot system suffers from a difficulty in that, since the concrete floor on which the work stations are provided is different in linear expansion coefficient from the rack engaged with the pinion of the robot, variations in the ambient temperature lower the accuracy in positioning the robot in place at the work stations.